Compute fg and bg colors for setEditable for StyledText

This commit adds the foreground and background color computation for
setEditable. Earlier this was handled only for setEnabled. This commit
also adds a different foreground and background color for StyledText
when background is not editable.

Fixes :#3132

Author: elsazac

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java

@@ -149,7 +149,7 @@ public class StyledText extends Canvas {
 	/** False iff the widget is disabled */
 	boolean enabled = true;
 	/** True iff the widget is in the midst of being enabled or disabled */
-	boolean insideSetEnableCall;
+	boolean insideUpdateColorsCall;
 	Clipboard clipboard;
 	int clickCount;
 	int autoScrollDirection = SWT.NULL;	// the direction of autoscrolling (up, down, right, left)
@@ -186,6 +186,8 @@ public class StyledText extends Canvas {
 	AccessibleAdapter accAdapter;
 	MouseNavigator mouseNavigator;
 	boolean middleClickPressed;
+	private static final RGB COLOR_DISABLED_STATE = new RGB(54, 54, 54);
+	private static final RGB COLOR_NON_EDITABLE_STATE = new RGB(48, 48,48);
 
 	//block selection
 	boolean blockSelection;
@@ -8287,11 +8289,13 @@ public void setBackground(Color color) {
 			}
 		}
 	}
-	customBackground = color != null && !this.insideSetEnableCall && !backgroundDisabled;
+	customBackground = color != null && !this.insideUpdateColorsCall && !backgroundDisabled;
 	background = color;
 	super.setBackground(color);
-	resetCache(0, content.getLineCount());
-	setCaretLocations();
+	if (content != null) {
+		resetCache(0, content.getLineCount());
+		setCaretLocations();
+	}
 	super.redraw();
 }
 /**
@@ -8772,6 +8776,54 @@ public void setDragDetect (boolean dragDetect) {
 	checkWidget ();
 	this.dragDetect = dragDetect;
 }
+
+/**
+ * Applies foreground and background colors based on the control's state.
+ * Custom foreground and background settings are preserved and not overridden.
+ *
+ * @param enabled  {@code true} if the control is enabled; {@code false} otherwise
+ * @param editable {@code true} if the control is editable; {@code false} otherwise
+ * @since 3.134
+ *
+ */
+protected void updateColors(boolean enabled, boolean editable) {
+	this.insideUpdateColorsCall = true;
+	Display display = getDisplay();
+	try {
+		if (enabled && editable) {
+			if (!customBackground) {
+				Color bg = display.getSystemColor(SWT.COLOR_LIST_BACKGROUND);
+				setBackground(bg);
+			}
+			if (!customForeground) {
+				Color fg = display.getSystemColor(SWT.COLOR_LIST_FOREGROUND);
+				setForeground(fg);
+			}
+		} else if (!enabled) {
+			if (!customBackground) {
+				Color bg = new Color(display, COLOR_DISABLED_STATE);
+				setBackground(bg);
+			}
+			if (!customForeground) {
+				Color fg = display.getSystemColor(SWT.COLOR_DARK_GRAY);
+				setForeground(fg);
+			}
+		} else if (!editable) {
+
+			if (!customBackground) {
+				Color bg = new Color(display, COLOR_NON_EDITABLE_STATE);
+				setBackground(bg);
+			}
+			if (!customForeground) {
+				Color fg = display.getSystemColor(SWT.COLOR_GRAY);
+				setForeground(fg);
+			}
+		}
+	} finally {
+		this.insideUpdateColorsCall = false;
+	}
+}
+
 /**
  * Sets whether the widget content can be edited.
  *
@@ -8785,28 +8837,13 @@ public void setDragDetect (boolean dragDetect) {
 public void setEditable(boolean editable) {
 	checkWidget();
 	this.editable = editable;
+	updateColors(this.enabled, this.editable);
 }
 @Override
 public void setEnabled(boolean enabled) {
 	super.setEnabled(enabled);
-	Display display = getDisplay();
 	this.enabled = enabled;
-	this.insideSetEnableCall = true;
-	try {
-		if (enabled && editable) {
-			if (!customBackground) setBackground(display.getSystemColor(SWT.COLOR_LIST_BACKGROUND));
-			if (!customForeground) setForeground(display.getSystemColor(SWT.COLOR_LIST_FOREGROUND));
-		} else if(!enabled) {
-			if (!customBackground) setBackground(display.getSystemColor(SWT.COLOR_TEXT_DISABLED_BACKGROUND));
-			if (!customForeground) setForeground(display.getSystemColor(SWT.COLOR_WIDGET_DISABLED_FOREGROUND));
-		} else if(!editable) {
-			if (!customBackground) setBackground(display.getSystemColor(SWT.COLOR_TEXT_DISABLED_BACKGROUND));
-			if (!customForeground) setForeground(display.getSystemColor(SWT.COLOR_LIST_FOREGROUND));
-		}
-	}
-	finally {
-		this.insideSetEnableCall = false;
-	}
+	updateColors(this.enabled, this.editable);
 }
 
 @Override
@@ -8882,11 +8919,13 @@ public void setForeground(Color color) {
 			}
 		}
 	}
-	customForeground = color != null && !this.insideSetEnableCall && !foregroundDisabled;
+	customForeground = color != null && !this.insideUpdateColorsCall && !foregroundDisabled;
 	foreground = color;
 	super.setForeground(color);
-	resetCache(0, content.getLineCount());
-	setCaretLocations();
+	if (content != null) {
+		resetCache(0, content.getLineCount());
+		setCaretLocations();
+	}
 	super.redraw();
 }
 /**